Message-ID: <cd5bae52c59264f52d98859b99a364797ad4655f.camel@cybertec.at>
Subject: Re: SQL Server's WITH (NOLOCK) equivalent in PostgreSQL?
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: "David G. Johnston" <david.g.johnston@gmail.com>, 
 =?UTF-8?Q?=EC=9D=B4=ED=98=84=EC=A7=84?=
	 <jemie9812@gmail.com>
Cc: "pgsql-general@lists.postgresql.org" <pgsql-general@lists.postgresql.org>
Date: Mon, 31 Mar 2025 09:58:41 +0200
In-Reply-To: <CAKFQuwYCj-gXZuyrwpP-jycbgH2_HmEsNWvJNDqr0WT2fEp8_A@mail.gmail.com>
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On Sun, 2025-03-30 at 22:10 -0700, David G. Johnston wrote:
> On Sunday, March 30, 2025, =EC=9D=B4=ED=98=84=EC=A7=84 <jemie9812@gmail.c=
om> wrote:
> > Since PostgreSQL uses MVCC, I'm wondering what the best practice is for=
 non-blocking reads,=20
> > and whether there's an equivalent to dirty reads or READ UNCOMMITTED.
>=20
> https://www.postgresql.org/docs/current/transaction-iso.html
>=20
> We are unable to implement read uncommitted because of our choice to impl=
ement MVCC.

Perhaps it would be better to say "there is no need to implement a READ UNC=
OMMITTED
isolation level that actually allows for dirty reads".  On databases like S=
QL Server
you don't use READ UNCOMMITTED because you desperately want to see dirty, i=
nconsistent
data.  It is just something you have to accept in order to avoid read locks=
.

Since PostgreSQL doesn't use read locks, there is no need for that.

Yours,
Laurenz Albe